Extinction of Counterflow Diffusion Flames With Fine-Water Droplets.
Extinction of Counterflow Diffusion Flames With
Fine-Water Droplets.
(781 K)
Lazzarini, A. K.; Krauss, R. H.; Chelliah, H. K.;
Linteris, G. T.
Halon Options Technical Working Conference.
Proceedings. HOTWC 2000. Sponsored by: University of
New Mexico, Fire Suppression Systems Assoc., Fire and
Safety Group, Great Lakes Chemical Corp., Halon
Alternative Research Corp., Hughes Associates, Inc.,
Kidde Fenwal, Inc., Kidde International, Modular
Protection, Inc., Next Generation Fire Suppression
Technology Program, Sandia National Laboratories, Summit
Environmental Corp., Inc. and 3M Specialty Materials.
May 2-4, 2000, Albuquerque, NM, 195-203 pp, 2000.
Available from:
For more information contact: Center for Global
Environmental Technologies, New Mexico Engineering
Research Institute, University of New Mexico, 901
University Blvd., SE, Albuquerque, NM 87106-4339 USA.
Telephone: 505-272-7250,
Fax: 505-272-7203. WEB:
http://nmeri.unm.edu/cget/confinfo.htm
Keywords:
halon alternatives; diffusion flames; extinction;
droplets; water; drop sizes; size distribution; water
vapor; halons
Abstract:
Basic investigations aimed at better understanding the
fire suppression mechanism of water dates back to the
1950s, while more recent studies have focused on water
mist systems. Although there is a consensus in the
literature on the fundamental fire suppression mechanism
of water, no detailed quanlitative information on the
various physical. thermal, and chemical effects of water
mist were available until recent modeling capabilities
were developed. The recent detailed modeling efforts
were primarily carried out in two configurations,
counter-flow and co-flow. The former flow configuration
provides a convenient approach to understanding the
interactions of fine-water droplets with flames,
including flame extinction conditions. For example,
investigations by Lentati and Chelliah have shown that
dilution of the air stream (or displacement of oxygen)
with saturated water vapor alone reduces the flame
extinction condition (characterized here by the flow
strain rate) of a methane-air non-premixed flame by
about 12%. Experimental results presented here support
such predictions. The further addition of water, in the
form of fine droplets, causes significant thermal
cooling of the flame front because of the relatively
large latent heat of vaporization of water. Addition of
3% of water by mass in the form of 20 mum monodisperse
droplets (the optimum size for this flow configuration)
was shown to reduce the extinction strain rate by an
additional 55%. By selectively excluding the source
terms contributing to the gas-phase and the condensed
phase conservation equations, the importance of thermal
effects associated with water mist was clearly
demonstrated. The chemical (e.g., shifting of the
water-gas equilibrium reaction and enhanced three-body
recombination effects) and other physical (e.g.,
modification of transport coefficients) effects
associated with fine-water droplets were shown to have a
minor effect.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899